Long-term assessment of anaerobic co-digestion of food waste and microalgae: Process stabilization, methane yield and agronomic properties of digestate
Iacy Maria Pereira de Castro, Thiago de Alencar Neves, André Pereira Rosa, Fernando França da Cunha, Fabiana Passos
Abstract
This study aimed at assessing the anaerobic co-digestion of food waste and microalgal biomass. Microalgae were harvested from an open treatment pond used for digestate treatment. For that, two continuous laboratory-scale reactors were operated over 200 days at ambient temperature. Results obtained showed that the reactor fed with a 75:25 mixture of food waste and microalgae (based on volatile solids) improved process stability, overcoming volatile fatty acid accumulation and pH drop, compared to mono-digestion of food waste. Consequently, co-digestion increased methane yield in 20–32 % (0.22 L CH 4 /g VS). Moreover, the agronomic assessment revealed that digestates exhibited potential for use as a biofertilizer, i.e. adequate organic matter and nutrient contents heavy metals concentrations below limits established by different regulations (i.e., Zn, Ni, Cr, and Cu). These findings indicate that the anaerobic co-digestion of food waste and microalgae may offer potential for biomass valorisation in a circular approach, generating bioenergy and biofertilizer. • Anaerobic digestion of food waste and its co-digestion with microalgae were examined. • Microalgae contributed to maintaining pH buffer capacity and process stability. • Co-digestion showed more stable and highest methane yield in all phases. • Digestates could be used as biofertilizer according to agronomic characterization.